Note that there are no Greater Bane weapons for mephits, as they are Neutral Outsiders and neither Elementals nor Magical Beasts.

Recommended Strategies
◦ Sor'jek can be moderately effectively surrounded and kept in one place by 4 or more durable (500+ hp) characters. He can force his way out via knockback attacks, but doesn't do so often.
◦ While locked in one general area, persistent AoE damage spells like Firewall are quite effective. ◦ They can be equally effective when soloing by simply circling him, or in a group by simply holding agro. He will not pursue his target, he has caster AI and thus will simply lob spells at ranged attackers.

◦ Many groups assign one (or more) players to kill all mephits on sight while the rest damage Sor'jek and try to hold him in place. However, the Syriana mephit can be completely ignored if desired.
◦ Mephit spawn rates seem to increase over time, but only one of each specific mephit will be active at one time.

So the key is to have blunt weapons to bypass his DR 50 (on elite). Fortunately I crafted a triple positive Greensteel Maul just to deal with Sorjek and other undead.